Glutamate-gated chloride channels, or H-receptors, have been identified in arthropod nerve and muscle (Lingle et al, 1981, Brain Res. 212: 481–488; Horseman et al., 1988, Neurosci. Lett. 85: 65–70; Wafford and Sattelle, 1989, J. Exp. Bio. 144: 449–462; Lea and Usherwood, 1973, Comp. Gen. Parmacol. 4: 333–350; and Cull-Candy, 1976, J. Physiol. 255: 449–464).
Invertebrate glutamate-gated chloride channels are important targets for the widely used avermectin class of anthelmintic and insecticidal compounds. The avermectins are a family of macrocyclic lactones originally isolated from the actinomycete Streptomyces avermitilis. The semisynthetic avermectin derivative, ivermectin (22,23-dihydro-avermectin B1a), is used throughout the world to treat parasitic helminths and insect pests of man and animals. The avermectins remain the most potent broad spectrum endectocides exhibiting low toxicity to the host. After many years of use in the field, there remains little resistance to avermectin in the insect population. The combination of good therapeutic index and low resistance strongly suggests that the glutamate-gated chloride (GluCl) channels remain good targets for insecticide development.
Glutamate-gated chloride channels have been cloned from the soil nematode Caenorhabditis elegans (Cully et al., 1994, Nature 371: 707–711; see also U.S. Pat. No. 5,527,703 and Arena et al., 1992, Molecular Brain Research. 15: 339–348) and Ctenocephalides felis (flea; see WO 99/07828).
In addition, a gene encoding a glutamate-gated chloride channel from Drosophila melanogaster was previously identified (Cully et al., 1996, J. Biol. Chem. 271: 20187–20191; see also U.S. Pat. No.5,693,492).
O'Tousa et al. (1989, J. Neurogenetics 6: 41–52) map photoreceptor mutations to the ChIII 92B region of the Droshphila genome.
Stuart, 1999, Neuron 22:431–433 reviews the art which suggests that histamine is an invertrbrate nuerotransmitter.
Despite the identification of the aforementioned cDNA clones encoding GluCls, including a previous identification of a Drosophila GluCl gene (see U.S. Pat. No. 5,693,492), it would be advantageous to identify additional genes which encode invertebrate ligand-gated ion channels, including but not limited to additional GluCls or other ligand-gated channels, such as a ligand-gated ion channel (LGIC) which is activated by histamine, which may provide additional targets for effective insecticides, in turn allowing for improved screening to identify novel LGIC modulators that may have insecticidal, mitacidal and/or nematocidal activity for animal health or crop protection. The present invention addresses and meets these needs by disclosing novel genes which express a Drosophila melanogaster ligand-gated ion channel, wherein expression of the respective Drosophila gene in Xenopus oocytes or other appropriate host cell results in an active LGIC. Heterologous expression of a respective LGIC(s) of the present invention will allow the pharmacological analysis of compounds active against parasitic invertebrate species relevant to animal and human health. Such species include worms, fleas, tick, and lice. Heterologous cell lines expressing an active LGIC can be used to establish functional or binding assays to identify novel LGIC modulators that may be useful in control of the aforementioned species groups.